Current Navy Sea Base plans call for a capability to launch and support the operations of a Marine Expeditionary Brigade (MEB) from the ships of the Sea Base. The Landing Craft Air Cushion (LCAC), an air-cushion vehicle, is the prime surface assault connector of the Sea Base. Unfortunately, current assets are not able to bring the necessary number of required LCACs into theater. Another problem involves how to load those LCACs to support the MEB in an efficient and timely manner. Current methods of loading LCACs at sea are cumbersome and time consuming. The current methods of loading LCACs from larger cargo ships at sea typically involve loading LCACs while they are in the water of driving them onto lightweight temporary platforms that are relatively small in size and subject to substantial motion as sea states rise.
Alternative approaches have been contemplated which would use a ship as both an LCAC Carrier as well as a transfer enabler for the Sea Base. Some of these approaches requires the carrier ship to ballast-down, as in a heavy lift ship, so that the LCACs can “fly” on and off the mother ship. Other approaches use large elevators to transfer the LCAC between the carrier ship and the water. Such approaches are complex and inefficient.
It is also desirable for two or more ships to have the capability to moor together while at sea. However, the forces creating the relative vertical motions between two or more ships are too powerful to be overcome by traditional mooring and fendering systems. To fight these forces would mean fighting the entire restorative buoyancy force. Aside from welding the ships together, this is virtually unachievable. Analysis shows the in Sea State 4, the upper requirement for Sea Base operations, the relative vertical movement between two ships moored together will be too great to allow the safe transfer of personnel and cargo.
For the loading and offloading of cargo, traditional roll-on/roll-off (RO/RO) ramps operate through the bow and stern of a ship. However this cargo transfer is typically performed between a ship and a pier, and the height of the pier is either known or at least within a specific range. For ships at sea, it is extremely difficult to moor two or more ships bow to stern so that a RO/RO evolution can occur. But in certain evolutions, such as at a Sea Base, a large number of vehicles must be transferred from one ship to another. While a crane can be used to move these vehicles, a RO/RO operation is much more efficient since the vehicles are in effect moving themselves between the ships. Since the ships cannot moor bow to stern, some sort of RO/RO system must be done transversely between two ships moored skin-to-skin at sea. But this introduces another problem in that the freeboard between ships can vary quite a bit, and ships with side-ports offer an even lower access point. It was previously thought impossible to develop a multi-purpose ramp (i.e., not ship-specific) that could accommodate the wide range of potential vertical heights of the various ships, which might want to transfer vehicles and/or personnel.